A light emitting diode (hereinafter referred to as “LED”) is capable of emitting high-illuminance light with a low level of electric power and is used as a light source for various kinds of electric devices such as a signal lamp and an illumination apparatus. In recent years, a blue LED as well as red and green LEDs is put into practical use. Light of many different colors can be generated by combining the red, green and blue LEDs. There is available a light emitting device using a plurality of LED light sources differing in emission color. The light emitting device complementarily controls the light intensity of the LED light sources and changes the chromaticity of mixed color light.
In this kind of light emitting device, if the deviation range of chromaticity of the LED light sources is wide, the deviation of chromaticity of the mixed color light grows larger. Thus the light colors of the light emitting devices manufactured differ from device to device. In general, the light having a chromaticity on the blackbody locus of chromaticity coordinates looks like white light in the sense of a human. On the other hand, if the chromaticity is deviated toward the deep ultraviolet side from the blackbody locus, the color difference is felt large and the light color looks unnatural.
There is known a variable chromaticity light emitting device capable of measuring the illuminance and chromaticity relative to an applied current with respect to individual light sources having different emission colors, feeding back the measurement results to correct the outputs of the respective light sources and consequently irradiating mixed color light with a desired chromaticity (see, e.g., Japanese Patent Application Publication No. 2004-213986 (JP2004-213986A)).
In the light emitting device disclosed in JP2004-213986A, however, a plurality of sensors and an expensive control unit having high operational performance are required in order to perform the feedback control by which a suitable mixing ratio is calculated and outputted using the measurement results of illuminance and chromaticity of the respective light sources. This may lead to an increased manufacturing cost.